And now Minnesota legislators are trying to make people more aware of the issue.

It is an issue Twin Cities resident Janet Thompson had no idea existed until two years ago.

"She had gone into the doctor because she had a lump on her breast. So they biopsied it and found out it was cancer," said her sister Lori Thompson-Garry.

Doctors diagnosed Thompson, who never smoked, with stage four lung cancer. Her doctor had a theory the sisters had never heard of.

"It's a pretty aggressive form of cancer and you're a non-smoker, it could be radon," Thompson-Garry recalls the doctor saying.

They tested her home where she lived for 15 years. Thompson-Garry remembers the radon numbers coming back around three or four times higher than the recommended EPA level.

Last year, Thompson died at age 49.

"It's a real awakening, a real eye opener that that danger is there," said State Representative Paul Anderson, a Republican from Starbuck.

Anderson, whose wife was close friends with Thompson, introduced "Janet's Bill". It would require Minnesotans to test their homes for radon when they put them up for sale unless he says they've tested in the last five years. It's one of two radon bills proposed at the state capitol this session.

"In our state, 1 out 7 homes has been tested so far and of those, 1 out of 3 has high levels of radon. So it's a pretty wide spread problem in Minnesota," said Anderson.

A Minnesota State Health Department map shows exactly how wide spread. It indicates most of the state has issues with radon. It's most prevalent in the south and west regions where officials claim 50-percent of the homes tested have elevated levels of radon above the EPA standards.

University of Minnesota professor Bill Angell is one of the leading experts in radon prevention and mitigation. He says right now there is little to no regulation in the state of Minnesota when it comes to radon. He believes there should be.

"We require smoke detectors and CO monitors in homes and radon is an even bigger risk," said Angell.

Radon is a natural occurring gas that develops in the soil, more so in Minnesota because of the type of geology in the Midwest. It can seep into your home's basement through cracks in the foundation.

According to the EPA, 21,000 people die from lung cancer caused by radon every year. That is second only to smoking. About 700 deaths in Minnesota have been attributed to radon says the state health department.

But Chris Galler with the Minnesota Association of Realtors is not convinced more regulation is the answer.

"We never said radon isn't a problem. It's more of how is the government is handling it and why are they burdening 5-percent of the population," said Galler of the number of people who buy and sell homes.

He adds Minnesotans selling their homes already have to inform potential buyers of any radon problems in a disclosure statement.

"The more forms consumers end up getting at each property," he said. "Pretty soon they don't read any of them."

Anyone can plead ignorance and check the box claiming they don't have radon issues in their home, according to Dan Tranter with the Minnesota Health Department.

"Any house has about a 40-percent chance at having a higher radon level," he said. "It's so important to get people to first understand it's an issue. There is a lot of misinformation out there."

That's why the health department has signed off on the other bill currently circulating the rooms of the state capitol authored by DFL Rep. Carolyn Laine, of Columbia Heights.

Her bill, the Radon Awareness Act, would require sellers to provide information to buyers about any history of radon testing and mitigation in the home, along with literature explaining the dangers of radon.

"It will have a clearer disclosure saying you should be aware of this, it is serious," said Laine.

Laine expects that bill to be voted on as early as Friday but most likely sometime next week.

The more aggressive "Janet's Bill" did not make it out of committee. Representative Anderson, however, vows to reintroduce it next year.

"If the radon awareness act would go through, it would only be the second radon specific law in Minnesota," said Tranter.

The first law changed the building code in 2009 forcing contractors to install a passive system that can help mitigate high levels of radon in new homes. But the health department warns people they should still test their new homes for radon. That's due to in part because the law is not completely fool proof, according to some.

"A lot of times, all they do is run a PVC pipe up, there's not an outlet, it's not run through the roof," said Mike Langer, owner of Langer Construction.

Langer is a certified radon mitigation installer. He believes as high as 50-percent of the systems in new homes he and his team come across have been installed incompletely.

The concept is simple. Crews install a pipe into the basement floor, run it out of the house, and use a fan to suck the radon gas up and out. It can cost anywhere from $800 to $2500. It could be more or less depending on the layout of your home.

"The only way to know is testing your house," said Langer.

You can have professionals test your home. Langer charges about $100. Or you can test your home yourself. Kits cost fewer than ten dollars.

"If its high in the house, you should think about mitigating it but it does not have to be done by tomorrow morning," said nuclear physicist and U of M professor John Broadhurst.

Broadhurst takes a more cautious approach when it comes to radon.

"The best thing to do is increasing the life span of the population. And I feel that needs some study work before one goes ahead and spends money modifying thousands, or maybe hundreds of thousands of dwellings," he said.

Still for many people testing is the best defense. Although the radon test was too late for Janet Thompson, her sister is speaking out in hopes others heed the same warnings.

"She would say, if I could just save someone else and then maybe it's worthwhile," said Thompson-Garry.